John 3:12

The expression "earthly things," some say is here used of the wind; that is, "If I have given you an example from earthly things, and ye did not even so believe, how shall ye be able to learn sublimer things?" And wonder not if He here call Baptism an "earthly" thing, for He calls it so, either from its being performed on earth, or so naming it in comparison with that His own most awful Generation. For though this Generation of ours is heavenly, yet compared with that true Generation which is from the Substance of the Father, it is earthly.

He does not say, "Ye have not understood," but, "Ye have not believed"; for when a man is ill disposed towards those things which it is possible to apprehend by the intellect, and will not readily receive them, he may justly be charged with want of understanding; but when he receives not things which cannot be apprehended by reasoning, but only by faith, the charge against him is no longer want of understanding, but unbelief. Leading him therefore away from enquiring by reasonings into what had been said, He touches him more severely by charging him with want of faith. If now we must receive our own Generation by faith, what do they deserve who are busy with their reasonings about that of the Only-Begotten?

"If I have told you earthly things, and ye believe not; how shall ye believe, if I tell you heavenly things?" What earthly things did He tell, brethren? "Except a man be born again;" is that an earthly thing? "The Spirit bloweth where it listeth, and thou hearest its voice, and knowest not whence it cometh, or whither it goeth;" is that earthly? For if He spoke it of the wind, as some have understood it, when they were asked what earthly thing the Lord meant, when He said, "If I told you earthly things, and ye believe not; how shall ye believe, if I tell you heavenly things?" Now what did He name earthly? He was speaking of the spiritual birth; and going on, saith, "So is every one that is born of the Spirit." Then, brethren, which of us does not see, for example, the south wind going from south to north, or another wind coming from east to west? How, then, know we not whence it cometh and whither it goeth? What earthly thing, then, did He tell, which men did not believe? Was it that which He had said about raising the temple again? Surely, for He had received His body of the earth, and that earth taken of the earthly body He was preparing to raise up. They did not believe Him as about to raise up earth. "If I told you earthly things," saith He, "and ye believe not; how shall ye believe if I tell you heavenly things?" That is, if ye believe not that I can raise up the temple cast down by you, how shall ye believe that men can be regenerated by the Spirit?

(Tr. xii. in Joan. c. 7) That is: If ye do not believe that I can raise up a temple, which you have thrown down, how can ye believe that men can be regenerated by the Holy Ghost?

A doctrine, saith He, not exceeding the understanding befitting man, ye from your extreme folly received not, and how shall I explain to you things more Divine? For they who in their own matters are most foolish, how shall they be wise in matters above them? And they who are powerless as to the less, how shall they not find the greater intolerable? And if, says He, ye believe not Me being Alone in speaking, but seek many witnesses for every thing, whom shall I bring to you as a witness of the heavenly Mysteries?

If you out of extreme foolishness did not receive a doctrine that does not exceed the understanding human beings are capable of, how can I explain things more divine? For if people are foolish in their own matters, how do they expect to be wise in matters above them? How do those who are powerless in lesser matters expect to find the greater things intolerable? And if, he says, you do not believe me when I speak alone but rather seek many witnesses for everything, whom shall I bring to you as a witness of the heavenly mysteries?

"If I have told you earthly things, and you do not believe," that is, if I told you about regeneration accomplished in baptism and you did not accept it, but asked "how?" (He calls this birth "earthly" because it takes place on earth for the benefit of people living on earth; although by grace and dignity it is heavenly, we are baptized while on earth). So if I spoke of this "earthly" birth and found you unbelieving, how will you believe if you hear of the ineffable heavenly birth by which the Only-begotten Son was born of the Father?
Some, however, understood "earthly" as referring to the example of the wind, so that the meaning of the passage is presented as follows: if I presented you an example from earthly things, and you were not convinced by it, then how can you learn things more exalted?

Thirdly, he rebukes him for his slowness because of the quality of the things under discussion. For it is not unusual when someone does not grasp difficult matters, but it is inexcusable not to grasp easy things. So he says, If I spoke of earthly things, and you did not believe, how will you believe if I tell you of heavenly things? As if to say: If you do not grasp these easy things, how will you be able to understand the progress of the Holy Spirit? "What is on earth we find difficult, and who will search out the things in heaven," as is said in Wisdom (9:10).

But one might object that the above does not show that the Lord spoke of earthly things to Nicodemus. I answer, according to Chrysostom, that the Lord's statement, If I spoke of earthly things, refers to the example of the wind. For the wind, being something which is generable and corruptible, is regarded as an earthly thing. Or one might say, again according to Chrysostom, that the spiritual generation which is given in baptism is heavenly as to its source, which sanctifies and regenerates; but it is earthly as to its subject, for the one regenerated, man, is of the earth.

Or one might answer, according to Augustine, that we must understand this in reference to what Christ said earlier: "Destroy this temple," which is earthly, because he said this about the temple of his body, which he had taken from the earth.

If I spoke of earthly things, and you did not believe, how will you believe if I tell you of heavenly things? As if to say: If you do not believe in a spiritual generation occurring in time, how will you believe in the eternal generation of the Son? Or, if you do not believe what I tell you about the power of my body, how will you believe what I tell you about the power of my divinity and about the power of the Holy Spirit?